In recent years, as an image display apparatuses (or devices) which replaces a cathode-ray tube (CRT) display apparatuses (or devices), flat displays such as a liquid crystal display (LCD), an electroluminescence display (ELD), and a plasma display panel (PDP) have been developed positively. Among these flat displays, the PDP has attracted the attention as an image display apparatus (or device) suitable for a large screen despite being a flat panel. However, in the flat panel such as PDP, whitening (or white flow) of an image (in particular dark image) occurs on the screen surface, resulting in deterioration of daylight contrast (or contrast of bright environment). Moreover, light reflex of an outside light in the inside of the panel generates a reflection of the outside light. In particular, the PDP can display an image clearly in a dark environment into which an outside light does not enter, however, the PDP has conspicuous tendency that a display image cannot be visually recognized under a daylight (or light room) environment. Therefore, in spite of having high display precision, the PDP needs a density filter (black mask) to be interposed between pixels, or a dimmer filter to be disposed in front of the panel. However, such a black mask or dimmer filter disposed only improves visibility in a relatively dark inside of a house, and does not sufficiently enhance contrast in a light environment (for example, an office, a store or outlet, the outside of a house). Moreover, since luminance (or brightness) of an image is reduced in these methods, these methods require high power consumption in order to increase luminance (or brightness).
Japanese Patent Application Laid-Open No. 196128/2002 (JP-2002-196128A) discloses an optical filter for PDP, which comprises a transparent base material (or support), and an antireflection film or an infrared ray-shielding filter layer, wherein the antireflection film or the infrared ray-shielding filter layer is formed on one side of the base material, and the antireflection film contains an inorganic fine particle and comprises two layers different in refractive index from each other. However, in this optical filter, in the case forming the antireflection film, a reflection of an outside light cannot be sufficiently inhibited or interrupted. Moreover, use of the infrared ray-shielding filter brings about decrease in image luminance.
Moreover, Japanese Patent Application Laid-Open No. 319351/2002 (JP-2002-319351A) discloses a plasma display device comprising a filter having a film-like front and an anti-glare layer which are directly attached on the front side of the panel, wherein, the filter has an anti-magnetic layer comprising a coloring matter-containing adhesive material or a metal film, and being formed on a transparent base film, and the anti-glare layer sprinkles diffusion matter. However, even in the device, it is impossible to inhibit a reflection of an outside light without reducing image luminance.
Incidentally, Japanese Patent Application Laid-Open No. 504627/1994 (JP-6-504627A) discloses a plastic louver film as a privacy screen film for covering a screen of CRT or other displays, wherein the plastic louver film comprises a transparent layer comprising a cellulose acetate butyrate (CAB), and a dark layer comprising a CAB and a carbon black. This document describes that the dark layer comprises a central zone (or section) having a relatively high absorption coefficient and an outer zone (or section) adjacent to the central zone and having a relatively low absorption coefficient, that a ghost image due to light reflection can be reduced, and that a person other than an operating personnel cannot read a displayed data.
Moreover, Japanese Patent Application Laid-Open No. 70834/1978 (JP-53-70834A) discloses a skivable billet and a skivable product thereof, wherein the billet alternately arrays a low optical density layer comprising a cellulose acetate butyrate and a relatively high optical density layer comprising a composite self-crosslinking anionic acrylate, a finely divided silica and a water-soluble polyazo direct dye.